The LIJOS system is a Lisp Implementation of the Java ObjectStream
protocol. That is, it is an implementation, in Lisp, of the Java
serializing ObjectStream protocol that supports the
(de)serialization of Java objects into and from appropriately
mapped Lisp objects.

Runs in ACL 5.0 but "intended to be very portable".

Also, while ACL is the "prefered" Lisp dialect, most of the
code is pretty vanilla CommonLisp/CLOS, and the ACL-dependent parts
(dealing primarily with wrappers around ACL's socket-implementation
and the definition of some numeric variables) are neatly packed away
in a couple files in a sub-directory (that is: I've not really had time
to work on ports to other lisp-implementations, but my intent is that
they would be pretty painless.)

The main page is here.
The executable code, documentation and examples for this pre-release (v1) version of the LIJOS system, for use with Allegro CommonLisp (v5.0) can be found at:
http://www.pointnclick.com/lijos/index.html (Windows and Sparc).

The license is pretty liberal ("Permission to use, copy, and distribute this software is hereby granted, provided that this copyright notice is retained in all copies.")